Abstract and Introduction

Abstract

Objective: Allopurinol dosing has frequently been limited based on creatinine clearance (CrCL), resulting in failure to achieve target serum urate (SU). The aim of this analysis was to determine how many milligrams of allopurinol above the recommended CrCL-based dose (R+) are required to achieve target SU and to investigate the factors that influence R+.

Methods: We analysed data from participants in a 24-month open, randomized, controlled, parallel-group, comparative clinical trial. Data obtained during the 12-month dose escalation (DE) phase of the study (year 1 for DE/DE and year 2 for control/DE) were combined. R+ dose was defined as the number of milligrams of allopurinol above the CrCL-based dose at the final visit.

Results: Of the 132 participants, R+ allopurinol dose at the final visit was ≤ 100 mg/day in 38 (28.8%), 101–200 mg/day in 46 (34.8%) and > 200 mg/day in 48 participants (37.1%). There was no significant difference between the R+ groups in the number of participants achieving target SU. There was an increase in plasma oxypurinol and a larger percentage and absolute change in SU as R+ increased. Multivariate analysis revealed CrCL, weight, baseline SU and allopurinol dose, were significantly positively associated with allopurinol dose at 12 months. There were no significant differences across R+ groups in renal or liver function adverse events, although there were numerically more serious adverse events in the higher R+ groups.

Introduction

Allopurinol remains the most commonly used urate-lowering therapy. Many clinicians have adhered to the creatinine-clearance (CrCL) based dosing recommendation published in 1984 by Hande et al.[1] believing that this will reduce the risk of the potentially fatal allopurinol hypersensitivity syndrome (AHS). However, while higher starting doses of allopurinol have been associated with AHS[2] there is little evidence that the maintenance dose, that is the dose of allopurinol required to achieve the widely recommended target urate,[3,4] is associated with AHS. Furthermore, a consequence of adopting a CrCL-based allopurinol dosing strategy is failure to achieve target serum urate (SU), with less than 20% of patients achieving SU < 6 mg/dL on such restricted doses.[5] We have recently published results of a randomized controlled trial showing that higher than CrCL-based allopurinol doses are safe and effective in people with gout.[6,7]

The aims of this pre-specified secondary analysis were to determine how much above CrCL-based allopurinol dose study participants required to achieve target SU, factors that influence the R+ requirement and identify any safety signal with higher R+ requirement.

Renal and liver function data are reported as the number of participants with at least one CTCAE adverse event in the 12-month dose escalation phase of the study. Serious adverse events are reported as the number of events (number of participants)R+ amount of allopurinol (milligrams) above creatinine clearance (CrCl)-based dose, GGT gamma-glutamyl transferase, ALP alkaline phosphatase, AST aspartate aminotransferase, ALT alanine aminotransferase

Tables

Table 4. Details of the nine participants who died during the dose escalation phase of the study

Competing interests Prof. Stamp reports grants from the Health Research Council of New Zealand during the conduct of the study; grants from Ardea Biosciences, grants from the Health Research Council of New Zealand, outside the submitted work; Dr Chapman has nothing to disclose: Prof. Barclay has nothing to disclose; Dr Horne reports grants from the Health Research Council of New Zealand during the conduct of the study; Prof. Frampton has nothing to disclose; Mrs Drake has nothing to disclose; Mr Tan has nothing to disclose; Prof. Dalbeth reports grants from the Health Research Council of New Zealand during the conduct of the study; grants from the Health Research Council of New Zealand, grants and personal fees from AstraZeneca, grants and personal fees from Ardea Biosciences, grants from Amgen, personal fees from Takeda, personal fees from Horizon and personal fees from Kowa, outside the submitted work.